Pinion angle when using m105 springs and zero degree perches. Should I use shims?

Hi guys,

i am just about done with the first phase of my bob project. The axle is mounted and the frame is cut.

While I was measuring the necessary drive shaft length I checked the pinion angle. It appears I have about 4 degrees of positive angle. I am using M105 trailer springs on zero degree 4 inch perches. I also pushed the axle back by about 15 inches.

The truck still needs the bed mounted and the cab extended so it is not yet fully loaded. I suspect the positive pinion angle will improve with more weight on the truck but I do not imagine by much.

i have searched and searched this subject and not found much talk about pinion angle. I would expect this to be a regular topic for those not using front deuce springs and perches.

Am I missing something here? I think the goal should be zero degree pinion angle like the front axle so I am considering shims.

i would love to hear from you who have bobbed your trucks. Did you shim to achieve your desired pinion angle? Is there a reason I should not be concerned with the positive pinion angle?

Thanks for your help.

You could go either way with it. You should be fine I have bobbed trucks both ways the angle isnt much.

I have the same question, so am bringing this up in hopes of having a more complete answer and discussion now that more people have bobbed them.

I too am using the M105 spring and it looks like there is maybe 8 degree. I could be wrong and it only be 4 degree as mentioned above, mine is not mounted yet on the frame. I'm plating the side of my frame and will go down 3" more with the L. I had 1/4 plate bent to make an 11" x 3" x 10' (2 pieces). My frame is uncut and the rear axle is going to be 53" from the back of an M105 bed (50" to center from end of the frame).

Do we need a tapered perch to bring the axle input to near parallel or at least what would be parallel when compressed? Design books say that the output and the input should be close to parallel to work best.

My M105 seemed to have nearly new springs, man they are heavy. I would like to remove a few leaves but will use the full spring pack for now. Less spring and an air bag would be nice.

To the bottom of the spring from the frame corner I have 9.5" with no load. I expected to build a perch from plates off the 105 adding another 1 3/8" height from spring bottom to axle, thus about 10 7/8". So then +3" = 13 7/8" would be my top of axle to the deuce frame measurement. How does that compare to others?

More information. I measured the angle of the spring mounting face at 5.36 degree upward facing. So to make it parallel with no load, I would need a spacer-saddle that tapers that amount. But under full deflection, that angle is less, so a taper that large would make it less than parallel (negative) on full deflection (which I expect to be rare).

I measured the front axle height from the frame and get right at 12". The height of the rear will determine if the back sits high, low or middle. I like an unloaded truck to have a slight angle forward, so the 13 7/8" measure above gives me a rear height that is 1 7/8" higher than the front. The reason I mention this is that I have some steel wedge materials that can serve as a spacer and give me at some angle. Over the length of a 6" piece, the height changes 1/4" and that calculates to 2.86 degree. If I use the tapered piece I can reduce the initial angle to 2.50 degree and loaded may be near flat. I may increase the angle a little more with a grinder.

At this point, I have talked myself into making taper of about 3 degree on my new axle perch.

I have these tapered steel bars that I'm making the axle perch with. Cut is made where it's 1" and at 6" long, it is 1 1/4". That calculates to about 2.8 degree. The block will have to be milled for bolt.

Hows that for a well fed cat.

tobyS said:

I have these tapered steel bars that I'm making the axle perch with. Cut is made where it's 1" and at 6" long, it is 1 1/4". That calculates to about 2.8 degree. The block will have to be milled for bolt.

Hows that for a well fed cat.

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I have put over 50,000 miles on my deuce since I bobbed it in 2006. Driven it from California to Florida towing a combined rolling weight of 32,000 lbs all on 105 Springs with welded 4 inch flat lift blocks. No pinion shim. I’ve wheeled the crap out of this truck. Beat on it profusely. I always grease every zerk fitting once a month. Change all the fluids once a year. And the oil every 4000 miles. You don’t need shims. Not saying they might help but I’ve nevr even questioned needing them.

Shannon, is it possible to take a side shot (picture) of the angle up on yours? Can you see the angle of the U-joint face and driveshaft on yours?

The M105 that my springs came off of was a rebuild that I believe had new springs. I can see once they are reassembled the middle of the spring will be compressed and that 9.5" space (uninstalled) will flatten a bit and end up 8.75"-9.0", so I will probably want a bit more block anyway. I'll go take a photo of the curve (at the bolt that holds them together) I'm talking about that I usually don't see on well used springs.

Thanks, toby

I’ll take a picture tomorrow in the day light.

Here are the pictures.

Thanks Shannon for taking those photo's. It's difficult to see the driveshaft angle in relation to the angle of the pinion, but it appears to point about straight to the output of the TC, somewhat up hill. Picture 3 makes it look like it could angle up 10 degree.

When I search pinon angle, most of the threads are concerning axle wrap, especially when using the large tires. That is understandable, because they increase the torque on the axle a lot. The solutions were mostly a torsion issue and I didn't see any discussion of the pinion angles, except as it relates to axle torque (wrap) making it worse.

My friend with a machine shop builds funny cars...ha, ha,...and we talked about the pinion angles. His recommendation was to keep them as parallel as possible.

That large lift you have would seem to have a huge twisting effect (long lever) on the spring aka wrap. Have you ever had any "wrap" issues....you seem to say no but it sounds like your use is on road mostly. Several threads turn into builds of torsion bars with those high lifts.

I went with plating my frame (with L 11" x 3" x10') and getting 3" of height there, so don't need near the height that you have under the spring. The torque will not have as much leverage on my spring like the large lifts do. I have 2 3/4" high perch (axle housing to bottom of spring).

I'll use the 9" height I measure the spring bottom to the frame to calculate the axle to frame dimensions. I have 3" + 2 3/4" + 9" = 14 3/4". My front is 12" so I have 2 3/4" higher at the rear than the front. Is that too much??..now's my time to reduce the perch height if it is. Wheelbase is 165".

Shannon, will you measure the front axle to frame and back axle to frame on yours? Does your truck sit higher in the back than the front and would you change that if you were at my stage?

I was told by several driveshaft places to never exceed 3 degrees for cruising and high RPM uses.

That sounds reasonable letssled. I moved my project to this thread;

https://www.steelsoldiers.com/showthread.php?186540-Deuce-4x4-with-M105-reduced-spring-and-air-bag

Check out post number 8. I calculated the pinion angle using no or parallel blocks for the perch with the 105 springs and come up with 4.17 degree, so the angle is not as bad as I had originally thought (6-10). With my 2.8 degree blocks, that makes my pinion angle under 1.5 degree, which I'm very happy with.

Hey Toby, whats your transfer case output angle? Letssleds guy was most likely talking about no more than 3 degrees deviation from end to end of shaft. In other words, you want your transfer case shaft and pinion as parallel as possible, at ride height.

Thanks Jbulach. The transfer case seems level with the frame for both front and rear outputs. I don't think it is tilted back...that's not mentioned in what I read that I can recall (I'll do some searching). Yea, it would be relative to the angle of the TC.

If you have info that it is tilted let me know, not that there is much I could do at this point.

I must have been fairly accurate on the estimates for my spring angle, ending at about 1.4 degree in relation to the frame, it has a visual but low angle up with the weight of the truck on the springs. I'm very happy with the angle and think it was worth putting the 2.8 degree block in

Rear of truck on springs, no payload, is 2" higher than the front. That may leave room to rebuild the front springs and come up an inch....will have to see it on level ground and consider some new front weight. Front rebuild will include an 809 series hood, getting the fan back from the radiator, frame and plow connects..... so will need stronger front springs on phase 14 of this project, 13 is putting air lock diff in the rear while 15 will have to be the powered 105 trailer. "Money Pit" is living up to it's (don't know sex yet) name.

tobyS said:

Front rebuild will include an 809 series hood, getting the fan back from the radiator, frame and plow connects..... so will need stronger front springs on phase 14 of this project, 13 is putting air lock diff in the rear while 15 will have to be the powered 105 trailer. "Money Pit" is living up to it's (don't know sex yet) name.

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